The present invention relates to an improved slag tap, i.e., a device for tapping molten fluid from the hearth of a furnance. The tap is particularly useful in operations where the refractory lining, especially at the end of the duct from which the molten fluid is discharged is exposed to corrosive conditions, and hence prone to early failure.
The flow of molten slag discharged from slagging waste disposal furnaces produces particularly harsh conditions on refractory linings exposed to it because of the variable chemical and physical properties of such slag. While for purposes of convenience the molten residue is referred to as slag, it is to be understood as including also molten metal, glass and any non-combustible inorganic residue. Devices employing refractory lined metal conduits for tapping molten fluids normally have a short service life due to the rapid deterioration of the refractory lining caused by the harsh conditions to which they are exposed.
Examples of solid waste disposal systems which provide a particularly harsh environment for refractory linings are disclosed in U.S. Pat. Nos. 3,729,298, 3,801,082 and 3,806,335, all of which relate to processes and/or apparatus for simultaneously disposing of refuse and producing useful gases and molten slag residues. In the above-mentioned waste disposal processes, refuse is fed into the top portion of a vertical shaft furnace while oxygen is fed into the base of the vertical shaft furnace. The furnace has a combustion and melting zone or hearth at the base from which molten slag is continuously tapped, using a suitable tapping device, and then quenched in a water bath.
The slag tap is subject to severe deterioration because of the wide variation in the chemical composition and temperature of the molten stream being tapped. It is common to have to shut down the furnace at frequent intervals to rebuild the tap. There are no known refractories that are not subject to rapid wear by the continuous tapping of slag of varying composition and temperature. The discharge lip is most vulnerable to attack and it is not possible with conventional tapping devices to maintain the point of discharge fixed in space.
In processes which involve continuous tapping, the discharge end of the slag tap from which the melt falls into a receiver, such as a quench tank, must remain essentially fixed in space. If it does not remain fixed, the hot slag will not fall where intended.